Research on Bolt Joint Looseness Detection and Imaging Based on Flow-Induced Ambient Noise

Bolt joints are commonly used in aviation structures. Bolt looseness may bring serious safety risks to the entire structure. Online monitoring of bolt looseness is of great importance to the safe of aviation equipment. Active guided wave detection methods can identify the tightness status of bolts accurately. However, active guided wave detection methods require big and heavy excitation equipment, such as wave generator and power amplifier, which limit the application in many online detection scenarios. The random ultrasonic guided waves excited by the coupling between the airflow and the airframe during flight can propagate long distances in structures, which carry rich structural status information and have great potential for passive online detection. This study analyzes the propagation mechanism of guided waves in bolt joints, constructs a wave propagation path identification method based on cross-correlation of passive flow-induced guided waves, and proposes a bolt tightness imaging method based on the delay-and-sum, by which the bolt joint looseness detection is realized. The proposed method is demonstrated to be efficient via experimental results where both single-bolt and double-bolt joint structures are tested.